<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>

</head>
<body>

<div id="app">
  <button v-on:click="sayHi">click me</button>
</div>

<!--cdn-->
<script type="text/javascript" src="https://unpkg.com/vue"></script>
<script>
  var vm = new Vue({
    el: "#app",
    data: {
      message: "hi",
      items: [
        {message: "jackenLeu"},
        {message: "jackenLeu1"},
      ]
    },
    methods: {
      sayHi: function () {
        alert(this.message)
      }
    }
  });
</script>
</body>
</html>